Magnetic induction devices, including inductors, transformers and related devices, are employed in a wide range of electronic and magnetic applications. Examples of such applications in common use include power management applications, such as switched mode power supplies and driver circuits, for portable consumer electronic devices. Other example applications include digital isolators employed in various integrated circuit devices, as well as radio frequency power amplifiers for wireless transmitters, used for instance in cellular telephones, WiFi communication devices, and so on.
In many applications, an inductor coil having a large ratio between its inductance and DC resistance can provide much better circuit performance and reliability than coils have lower inductance/DC resistance ratios. One way of increasing this ratio is by reducing DC resistance, which can be accomplished by employing inductor coil tracks having large cross-sectional area. However, particularly in integrated circuit applications, significant interest exists in maintaining and even decreasing size of electronic components. For instance, smaller integrated circuit components typically results in higher component density (e.g., more transistors, transformers, rectifiers, etc., per unit area), which leads to increased processing power, increased memory storage, or the like for a given size integrated circuit chip. Similar benefits can be achieved for miniaturizing integrated power modules, switched mode power supplies and driver circuit applications. Moreover, many applications such as mobile phones, digital cameras, and so forth, have size, weight and component density requirements that must be met by individual components or groups of components. In some applications, reduced size can also lead to reduced cost, higher component reliability, or a simplified and flexible design. Accordingly, though increasing cross-sectional area can provide reduced DC resistance, detrimental effects can occur as well since increased cross-sectional area usually results in increasing overall component size. Further, design or cost constraints may limit the cross-sectional area to a maximum.
One mechanism for achieving miniaturized and highly integrated power modules is the monolithic magnetic induction device. Monolithic integration of an inductor coil and silicon substrate has been used to enable a coil to be formed side-by-side with other circuit components, sometimes reducing substrate surface area consumption. Additionally, similar integrated circuit processes employed for transistors and other integrated circuit components can be utilized at least in part to form the monolithic inductor. This can reduce the inductor cost, facilitate simpler and more flexible mass production, as well as other benefits (e.g. reduced parasitics). As further surface area reduction is required beyond what these area consumption savings can provide, alternative or additional technologies may be required instead. One direction of modern research and development is to identify efficient ways of further reducing surface area consumption for inductor devices as well as integrated circuits alike.